Several methods are presently being developed to sense presence of a target molecule having a small or modest concentration in a fluid. However, estimation of the concentration of the target molecule is unavailable, where the fluid is substantially motionless relative to the sensor, in part because the fluid in equilibrium will have substantially the same concentration everywhere. At least two questions should be answered here: (1) Is the target molecule present in the fluid; and (2) If the target molecule is present, what is its estimated initial concentration?
What is needed is a nanotechnology approach that works with fluids (liquids and gases) to determine whether a target molecule is present in the fluid, and when the target molecule is present, to estimate an initial concentration of this substance. Preferably, the approach should allow a distinction to be made, in appropriate circumstances, between presence of first and second different target molecules and should indicate when the target molecule is attached to, and has saturated, a sensor. Preferably, the approach should distinguish between presence of a given target molecule and presence of a molecule that competes with the target molecule for attachment.